Hydroforming assembly of annular metallic uranium foil targets for Mo-99 production

Technetium-99m, the most widely used diagnostic radioisotope in nuclear medicine, is obtained from the decay of molybdenum-99 produced by neutron irradiation of uranium-235. Annular low-enriched uranium (LEU) targets employ a thin metallic uranium foil positioned between concentric aluminum tubes, requiring effective consolidation to minimize interfacial gaps and maintain adequate heat transfer during irradiation. Traditionally, the consolidation is achieved mechanically using a draw plug. This study evaluates hydroforming as a technically feasible alternative that applies direct radial pressure while avoiding plug-tube sliding contact. A dedicated system was developed to apply pressures from 4 to 60 MPa, and residual gaps were measured circumferentially at one central axial cross-section. At 60 MPa, the two nickel-foil-wrapped targets exhibited average gaps of approximately 10.6 and 6.7 μm and maximum gaps of 16 μm. A target using electrodeposited nickel showed an average gap of 6.4 μm and a maximum gap of 12 μm. Relative to the nominal initial assembly clearances, the corresponding average-gap reductions were approximately 84%, 90%, and 91%. Hydroforming also eliminates the specific scratching and galling mechanism associated with direct draw-plug contact. However, a direct statistical comparison of average gaps with the previous draw-plug route is not possible because different sampling protocols were used. The electroplated condition was evaluated in only one specimen, and the measurements do not establish full axial uniformity. The results demonstrate technical feasibility and substantial local gap reduction, while target-specific thermal analysis, axial assessment, and post-irradiation disassembly qualification remain necessary.